Periodically 79

I am periodically the number 79. Long ago some attempted to make me from 29, but learned it couldn't be done. If you add me to 80 I appear to be 47 temporarily.
What am I?

Answer

Gold
Gold is represented by the number 79 on the Periodic table of elements. Long ago alchemists tried to make gold from copper.(number 29) If you add gold to mercury (number 80) it will appear to be silver for a time.Hide